The projected shell model implements shell model configuration mixing in the projected deformed basis. Our analysis on the recently observed superdeformed band in ${}^{36}\mathrm{Ar}$ suggests that the neutron and proton 2-quasiparticle and the 4-quasiparticle bands cross the superdeformed ground band at the same angular momentum. This constitutes a picture of band disturbance in which the first and the second band crossing, commonly seen at separate rotation frequencies in heavy nuclei, occur simultaneously. We also attempt to understand the assumptions of two previous theoretical calculations which interpreted this band. Electromagnetic properties of the band are predicted.

A systematic study of the temperature dependence of the shapes and pairing gaps of some isotopes in the rare-earth region is made in the relativistic Hartree-BCS theory. Thermal response to these nuclei is always found to lead to a phase transition from the superfluid to the normal phase at a temperature $T_{\Delta }\sim 0.4–0.8$ MeV and a shape transition from prolate to spherical shapes at $T_c\sim 1.0–2.5$ MeV. These shape transition temperatures are appreciably higher than the corresponding ones calculated in the nonrelativistic framework with the pairing plus quadrupole interaction. Study of nuclei with continued addition of neutron pairs for a given isotope shows that with increased ground state deformation, the transition to the spherical shape is delayed in temperature. A strong linear correlation between $T_{\Delta }$ and the ground state pairing gap ${\Delta }^0$ is observed; a well-marked linear correlation between $T_c$ and the ground state quadrupole defromation ${\beta }_2^0$ is also seen. The thermal evolution of the hexadecapole deformation is further presented in the paper.

A novel experimental approach has been employed for the measurement of $\beta$-delayed protons from ${}^{24}\mathrm{Si}$ produced via the fragmentation of a ${}^{28}\mathrm{Si}$ beam with an energy of 100 MeV/nucleon. The secondary beam of ${}^{24}\mathrm{Si}$ was separated by the projectile fragment separator RIPS at RIKEN and was implanted in a 2.6 $\mu \mathrm{m}$ aluminum foil placed parallel to a gas-$\Delta E$ and silicon-$E$ detector telescope for the measurement of delayed protons. The above arrangement has led to a very clean, $\beta$-ray background free delayed proton energy spectra and a few new proton peaks could be identified from the decay of ${}^{24}\mathrm{Si}.$

Odd-even staggering of binding energies is studied in finite fermion systems with pairing correlations. We discuss contributions of the pairing and mean field to the staggering, and we construct the binding-energy indicators which measure the magnitude of pairing correlations and the effective single-particle spacings in a given system. The analysis is based on studying several exactly solvable many-body Hamiltonians as well as on the analytical formulas that can be applied in the weak and strong pairing limits.

Beta decay of neutron-rich ${}^{116}\mathrm{Rh}$ has been studied at the IGISOL facility using β-γ and γ-γ coincidence spectroscopy. Online mass separated ${}^{116}\mathrm{Rh}$ sources were produced by applying 25 MeV proton induced fission of natural uranium and the fission ion guide. Extended decay schemes have been constructed for the low- and high-spin states of ${}^{116}\mathrm{Rh},$ respectively. Two excited $0^{+}$ states in ${}^{116}\mathrm{Pd}$ at 1109.8 and 1732.9 keV are proposed as the quasi-β and intruder bandheads, respectively. New ${}^{116}\mathrm{Pd}$ data support a different bandhead at 1809.9 keV for the recently reported negative-parity band. The systematics of low-lying collective and two-quasiparticle levels in even Pd nuclei has been extended substantially. The behavior of the quasi-γ band in ${}^{116}\mathrm{Pd}$ reveals some deviation from a strict O(6) limit of the IBA model.

The $\gamma$-absorption cross section [i.e., giant dipole resonance (GDR)] of ${}^{106}\mathrm{Sn}$ is calculated at temperature $T=2\mathrm{}$ MeV and angular momenta $J=40\mathrm{}$ and 55 following the linear response theory at finite temperature and incorporating the thermal shape as well as orientation fluctuation corrections within the static path approximation approach. The orientation fluctuation corrections have been included for the first time in such a calculation, and are found to be rather unimportant. Then without the inclusion of these effects the GDR is calculated at several more temperature and spin values. We find that at $T=4\mathrm{}$ MeV the GDR width $\Gamma$ shows an increase of only about 1.5 MeV compared to its value at $T=0.5\mathrm{}$ MeV. However, at a fixed temperature $T=2\mathrm{}$ MeV, the increase in the width at $J=69\mathrm{}$ is by about 3 MeV compared to its value at $J=0.\mathrm{}$ Finally, we have also compared the increase of $\Gamma$ at $T=2\mathrm{}$ MeV as a function of J for ${}^{106}\mathrm{Sn}$ and ${}^{120}\mathrm{Sn}.$ The increase is steeper for the lighter isotope, as expected.

For the first time Borromean nucleus induced reactions have been measured below the three-body breakup threshold. A set of angular distributions for the single and two neutron transfer as well as on the charge exchange reaction channel has been obtained. The experimental data have sufficient angular coverage and precision to allow for the discrimination between different model predictions, which do not suffer from ambiguities introduced to the interpretation of experimental data due to flux losses into the three-body breakup channel. The viability of the idea is demonstrated in the case of nuclear reactions induced by the simplest Borromean nucleus, i.e., ${}^6\mathrm{He},$ on a structureless target, i.e., protons. Comparison with different theoretical approaches suggest that coupled channel effects play an important role. A decrease of the model wave function’s rms radius of 0.15 fm alters the predicted angular distributions such that they no longer follow the experimental results.

We study low-energy virtual Compton scattering off the proton within the framework of a nonrelativistic constituent quark model. The Compton tensor is divided into two separately gauge-invariant contributions. The first consists of the ground-state propagation in the direct and crossed channels together with an appropriately chosen term to satisfy gauge invariance. The residual part contains the relevant structure information characterized by the so-called generalized polarizabilities. We discuss two different schemes to obtain the generalized polarizabilities from the residual term. Explicit predictions for the generalized polarizabilities are presented for the Isgur-Karl model. Our results are compared with previous predictions in that model as well as other approaches.

The propagation of the lightest mesons in hadronic matter is studied at finite temperature, by including Dirac sea effects. The meson-nucleon interaction is described in a field theory model, which exhibits a residual interaction beyond the ground state, with a medium dependent coupling constant. The effective meson masses, the low lying collective excitations of nuclear matter, and the giant isoscalar resonances of a system with finite particle number are studied and compared with other theoretical predictions. The effect of different regularization prescriptions is also considered.

We study the isospin singlet pairing in asymmetric nuclear matter with nonzero total momentum of the condensate Cooper pairs. The quasiparticle excitation spectrum is fourfold split compared to the usual BCS spectrum of the symmetric, homogeneous matter. A twofold splitting of the spectrum into separate branches is due to the finite momentum of the condensate, the isospin asymmetry, or the finite quasiparticle lifetime. The coupling of the isospin singlet and triplet paired states leads to further twofold splitting of each of these branches. The gap equation is solved numerically in the isospin singlet channel in the case where the pairing in the isospin triplet channel and the renormalization of the single particle energies are neglected. We find nontrivial solutions with finite total momentum of Cooper pairs. The corresponding condensate has a periodic spatial structure which carries a isospin density wave at constant total number of particles. The phase transition from the BCS to the inhomogeneous superconducting phase is found to be first order and occurs when the density asymmetry $\alpha \equiv \left({\rho }_n-{\rho }_p\right)/({\rho }_n+{\rho }_p)$ (defined in terms of partial densities of neutrons ${\rho }_n$ and protons ${\rho }_p)$ is increased above 0.25. The transition from the inhomogeneous superconducting to the unpaired normal state is second order. The maximal values of the critical total momentum (in units of the Fermi momentum) and the critical density asymmetry at which condensate disappears are $P_c{/p}_F=0.3\mathrm{}$ and ${\alpha }_c=0.41\mathrm{}$ (assuming free single particle spectrum). The possible spatial forms of the ground state of the inhomogeneous superconducting phase are briefly discussed.

Using a recently proposed classification scheme for phase transitions in finite systems [Phys. Rev. Lett. 84, 3511 (2000)] we show that within the statistical standard model of nuclear multifragmentation the predicted phase transition is of first order.

Experimental joint multiplicity distributions of neutrons and charged particles provide a striking signal of the characteristic decay processes of nuclear systems following energetic nuclear reactions. They present, therefore, a valuable tool for testing theoretical models for such decay processes. The power of this experimental tool is demonstrated by a comparison of an experimental joint multiplicity distribution to the predictions of different theoretical models of statistical decay of excited nuclear systems. It is shown that, while generally phase-space based models offer a quantitative description of the observed correlation pattern of such an experimental multiplicity distribution, some models of nuclear multifragmentation fail to account for salient features of the observed correlation.

It is shown that a particle-rotor model description of rotational bands in odd nuclei, built upon the $K=1/2\mathrm{}$ pseudo-orbital singlet Nilsson state belonging to the shell with an even principal pseudo-oscillator quantum number, can be reformulated as a realization of partial supersymmetry.

The microscopic mechanism of identical normally deformed bands at low spin in the rare-earth nuclei is investigated using a particle-number conserving (PNC) treatment of the cranked shell model Hamiltonian. The observed identical seniority-zero, -one, and -two bands are reproduced quite well by the PNC calculation, in which no free parameter is involved. The influence of blocking effects on moments of inertia depends sensitively on the location and Coriolis response of the blocked levels. The crucial point is that the blocking effect must be taken into account strictly and consistently for the identical bands.

We present a charge-dependent one-boson-exchange nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ potential that fits the world proton-proton data below 350 MeV available in the year 2000 with a ${\chi }^2$ per datum of 1.01 for 2932 data and the corresponding neutron-proton data with ${\chi }^2/\mathrm{datum}$ $=1.02\mathrm{}$ for 3058 data. This reproduction of the $\mathrm{NN}$ data is more accurate than by any phase-shift analysis and any other $\mathrm{NN}$ potential. This is achieved by the introduction of two effective $\sigma$ mesons the parameters of which are partial-wave dependent. The charge dependence of the present potential (which we call “CD-Bonn”) is based upon the predictions by the Bonn full model for charge symmetry and charge-independence breaking in all partial waves with $J<~4.$ The potential is represented in terms of the covariant Feynman amplitudes for one-boson exchange which are nonlocal. Therefore, the off-shell behavior of the CD-Bonn potential differs in a characteristic way from commonly used local potentials and leads to larger binding energies in nuclear few- and many-body systems, where underbinding is a persistent problem.

A simple analytical expression is introduced for the average neutron multiplicity depending on the fission fragment mass using directly the prompt neutron energy spectrum in the framework of statistical theory of neutron evaporation from fission fragments. The theoretical results are compared with the experimental data for the spontaneous fission of ${}^{252}\mathrm{Cf}.$ The possibility of oscillative character of neutron average multiplicity versus fragment masses is discussed in terms of the neutron average binding energy for a given fragment mass.

Influence of asymmetry on superfluidity of nuclear matter with triplet-singlet pairing of nucleons (in spin and isospin spaces) is considered within the framework of a Fermi-liquid theory. Solutions of self-consistent equations for the critical temperature and the energy gap at $T=0\mathrm{}$ are obtained with the use of Skyrme effective nucleon interaction. It is shown that if the chemical potentials of protons and neutrons are determined in the approximation of ideal Fermi-gas, then the energy gap for some values of density and asymmetry parameter of nuclear matter demonstrates double-valued behavior. However, accounting for the feedback of pairing correlations through the normal distribution functions of nucleons, two-valued behavior of the energy gap turns into universal one-valued behavior. At $T=0\mathrm{}$ superfluidity arises and disappears as a result of a first order phase transition in density.

Excited states in ${}^{165}\mathrm{Ta}$ were populated in the ${}^{142}\mathrm{Nd}{(}^{27}\mathrm{Al}{,4n)}^{165}\mathrm{Ta}$ and ${}^{141}\mathrm{Pr}{(}^{28}\mathrm{Si}{,4n)}^{165}\mathrm{Ta}$ reactions and investigated using the AFRODITE array. The yrast rotational decay sequence up to spin ${53/2}^{-}$ is identified and assigned to the $\left[514\right]{9/2}^{-}$ configuration. The nuclear shape is investigated using total Routhian surface calculations. The experimental results are discussed in relation to existing data in the neighboring Ta isotopes and results from cranked shell model calculations. Unexpectedly large signature splitting, for a high-$\Omega$ configuration, is observed in the yrast band. Further discrepancies are observed between theoretical and experimental values for the band crossing frequency and signature splitting of the $B\left(M1\mathrm{}\right)/B\left(E2\mathrm{}\right)\mathrm{}$ ratios. The possibility that these discrepancies are a consequence of a large deviation from an axially symmetric nuclear shape is investigated.

We apply a quark interchange model to spin-dependent and exotic meson-meson scattering. The model includes the complete set of standard quark model forces, including one-gluon exchange spin orbit and tensor and scalar confinement spin orbit. Scattering amplitudes derived assuming simple harmonic oscillator (SHO) and Coulomb plus linear plus hyperfine meson wave functions are compared. In $I=2\mathrm{}$ $\pi \pi$ we find approximate agreement with the S-wave phase shift from threshold to 1.5 GeV, where we predict an extremum that is supported by the data. Near threshold we find a rapid energy dependence that may reconcile theoretical estimates of small scattering lengths with experimental indications of larger ones based on extrapolation of measurements at moderate $k_{\pi }^2.$ In pseudoscalar-vector scattering we find that the quark-quark $L\cdot S$ and T forces map onto $L\cdot S$ and T meson-meson interactions, and the P-wave $L\cdot S$ force is large. Finally we consider scattering in $J^{{\mathrm{PC}}_n}$ exotic channels, and note that some of the “Deck effect” mechanisms suggested as possible nonresonant origins of the ${\pi }_1\mathrm{}\left(1400\right)\mathrm{}$ signal are not viable in this model.